ACTG 356 is a three part, phase I/II open label protocol to compare Zidovudine, 3TC and Nevirapine (triple therapy-Part A) to Zidovudine, 3TC, 1592U89, and Nevirapine (quadruple therapy-Part B) or d4T, 3TC, Nevirapine and Nelfinavir (another quadruple therapy-Part C) in one of seven cohorts. Cohort 1 (Part A) includes patients less than or equal to 15 days to less than or equal to 3 months. Cohort 2 (Part A) includes patients greater than 3 months to less than or equal to 2 years. Cohorts 3 and 4 receive quadruple therapy as listed above in Part B. Cohort 3 includes patients greater than or equal to 30 days and less than or equal to 3 months. Cohort 4 includes patients greater than or equal to 3 months to less than or equal to 2 years. Cohort 5, 6 and 7 patients receive the quadruple therapy listed in Part C. Cohort 5 contains patients greater than or equal to 15 days and less than or equal to 3 months. Cohort 6 includes patients greater than 3 months and less than or equal to 2 years. Cohort 7 includes patients greater than or equal to 15 days and less than or equal to 3 months.